The present invention relates to a vehicle following apparatus which enables a vehicle to automatically follow a preceding vehicle running ahead thereof while optically measuring the distance thereto.
Examples of an optical distance detecting apparatus utilizing image sensors are known from Japanese Patent Publication Nos. 63-38085 and 63-46363. As illustrated in FIG. 7, the apparatuses disclosed therein commonly have a pair of first and second parallel optical systems having two convex lenses 101, 102 disposed in a horizontally aligned relation at a prescribed distance L away from each other. A pair of separate image sensors 103, 104 are horizontally disposed at focal points of the lenses 101, 102 at a distance f from the locations of corresponding lenses 101, 102, respectively, for generating respective image signals to a common signal processor 120. The signal processor 120 successively shifts the image signals from the image sensors 103, 104 and electrically superposes them one over the other, so that the distance R from the lenses 101, 102 to an object 121 is calculated based on the principle of triangulation using the following formula: EQU R=(f.times.L)/d
where d is a shift distance by which the image signals are moved to obtain the best match.
On the other hand, a typical method of following a preceding vehicle using image sensors or the like is disclosed in Japanese Patent Publication No. 60-33352. In this method, for the purpose of following a target on a display screen, an operator has to set a following gate or window on the display screen which encloses the target to be followed, while looking at the screen.
With the distance detecting apparatus as described above, the distance to an object is measured on the basis of a comparison between a pair of images sensed by the pair of optical systems including the image sensors. Accordingly, in cases where this apparatus is mounted on a vehicle for measuring the distance to a preceding vehicle, it is difficult for the driver to precisely determine to which vehicle the distance measurement is being effected if there are a plurality of preceding vehicles.
In addition, let us consider the case in which the above-described vehicle following method is used in combination with the above-described distance detecting apparatus for the purpose of following a preceding vehicle. In this case, if a vehicle provided with the distance detecting apparatus runs on a bad road having relatively large surface irregularities and bounces, a window defined on a display screen for following the preceding vehicle is forced to displace in the vertical direction, so that it loses sight of the preceding vehicle and becomes unable to perform a stable and reliable vehicle-following operation. Likewise, if the vehicle is travelling on a curved road, the vehicle following window is caused to displace sidewise to the right or left, thus resulting in the same situation as described above.